1. Field of the Invention
This invention relates to a process for decreasing the melt index and increasing the melt viscosity and melt elastically of polyamide compositions. More particularly, this invention relates to such a process in which the increase in melt elasticity and/or melt viscosity is effectuated by the addition of an effective amount of an aryl phosphoryl azide compound. Polyamide compositions treated in accordance with the process of this invention are capable of being fabricated into useful shaped articles of manufacture, e.g., filaments, both mono- and multifilament, films, tapes, ribbons, rods, laminates, and the like.
2. Description of the Prior Art
Polyamide compositions are disclosed in the prior art as having many and varied uses in industrial and commercial applications. For example, these polymers can be formed in filaments in which the polymer chains are oriented along the filament axis. Such filaments have many uses, in commercial application as for example in the production of fibers for tire cord, textiles and the like. Similarly, these polymers can be fabricated into other useful shaped articles, as for example, gears, lawn mower housings, skate boards and the like.
The melt index of polyamide compositions provides an indication of the viscosity of the polyamides, and their molecular weights. In general, polymers having low melt indexes are desirable because of improved properties of fibers and other shaped articles made therefrom. For example, fibers made from polymers of relatively low melt indexes have increased tensile strength, durability and impact resistance. These properties are very desirable, especially in fibers used as reinforcement for pneumatic automobile tires.
Several processes have been proposed in the prior art for increasing the viscosity and molecular weight of polyamides, as for example poly(hexamethylene adipamide). One such method is set forth in U.S Pat. No. 3,763,113 which discloses a method for increasing the molecular weight of polyamides having recurring -CONH-alkylene-NHCO-alkylene units, such as poly(hexamethylene adipamide) by heating the polyamide with a phosphonic acid derivative in the presence of an inert gas, such as nitrogen. Similarly, U.S. Pat. Nos. 3,551,548 and 3,763,113, each broadly describes a method for increasing the relative viscosity of polyamides, generally, and poly(hexylmethyleneadipamide), specifically, by sweeping a molten mixture of the polyamide and phosphorous compound with an inert gas.
Each of these processes provides various adverse effects. For example, in each of the processes an inert gas is employed, which in high concentrations cause uneven finishing, i.e. a variation in the degree of polymerization, throughout the polyamide, which results in a non-uniform polymer. Furthermore, inert gas is expensive, and require additional equipment and monitoring which can increase the cost of commercialization of the process, even though the inert gas is used in small amounts.
U.S. Pat. No. 4,417,032 discloses a process for forming quasi-random copolymers from two or more homo polyamides. In this process, the homo polyamides are melt blended in the presence of a phosphite promoter.
U.S. Pat. No. 3,509,107 discloses a process for increasing the relative viscosity of polyamide fibers or copolyamides by incorporating a phosphorous or phosphite compound into the polyamide under an inert gas atmosphere. The primary object of U.S. Pat. No. 3,509,107 is to provide a process for increasing the viscosity of polyamide yarn and cord which requires a minimum amount of gas. U.S. Pat. No. 3,551,548 (Brignac et al., 1970) describes various optimizing procedures for U.S. Pat. No. 3,509,107. The described patents are each directed only to a method of producing polyamide yarn with increased viscosity via incorporating a phosphorous or phosphite compound into the yarn, and then heating said yarn in the presence of inert gas.
British Patent No. 569,184 discloses a method for producing a random copolymer from nylon 6 and nylon 6,6. The invention described herein teaches that heating a mixture of nylon 6 and nylon 6,6 results in interchange between various sections of the respective polymer molecules with the final product being a random copolymer of nylon 6 and nylon 6,6. In order to produce a random copolymer of nylon 6 and nylon 6,6,British Patent No. 569,184 teaches that it is necessary to heat the mixture of homopolymers for periods of time up to 8 hr. at 285.degree. C. without any catalyst.
U.S. Pat. No. 4,390,667 discloses a process for decreasing the melt index and increasing the viscosity of polyamide fibers via incorporating a phosphate compound into the polyamide and heating the polylamide until the desired changes in the melt index and viscosity occur. The phosphate utilized in U.S. Pat. No. 4,390,667 include substituted aryl phosphates which satisfy certain Hammett sigma values
U.S. patent application Ser. No. 280,563 now abandoned teaches that polymers of caprolactam with increased viscosity may be produced by reacting in the melt a phosphite compound and a caprolactam polymer.
U.S. Pat. No. 4,417,031 discloses a process for preparing block and graft copolymers. The described process involves reacting two or more polyamides, polyesters, and homopolymers of .beta.-unsaturated carboxylic acids in order to form a graft and/or block copolymer. Included in the patent are copolymers formed from poly(caproamide) and poly(hexamethylene adipamide).
Diphenyl phosphoryl azide has been used as a convenient reagent for racemization-free peptide synthesis and for polymerization of peptides such as .beta.-alanine and L-alanylglycine. See for example, Nishi Nori et al. "Polymerization of Amino-acids or Peptides with Diphenyl Phosphoryl Azide (DPPA)", Int. J. Biol-Macromol., Vol. 2 pp. 53 (1980) and Shiori Takayuki et al., "Diphenylphosphoryl Azide. A New Convenient Reagent For A Modified Curtius Reaction and for the Peptide Synthesis", J. of The American Chemical Society, Vol. 94 pp. 6203-6205 (1972).